Survival of Escherichia coli in the environment: fundamental and public health aspects

In this review, our current understanding of the species Escherichia coli and its persistence in the open environment is examined. E. coli consists of six different subgroups, which are separable by genomic analyses. Strains within each subgroup occupy various ecological niches, and can be broadly characterized by either commensalistic or different pathogenic behaviour. In relevant cases, genomic islands can be pinpointed that underpin the behaviour. Thus, genomic islands of, on the one hand, broad environmental significance, and, on the other hand, virulence, are highlighted in the context of E. coli survival in its niches. A focus is further placed on experimental studies on the survival of the different types of E. coli in soil, manure and water. Overall, the data suggest that E. coli can persist, for varying periods of time, in such terrestrial and aquatic habitats. In particular, the considerable persistence of the pathogenic E. coli O157:H7 is of importance, as its acid tolerance may be expected to confer a fitness asset in the more acidic environments. In this context, the extent to which E. coli interacts with its human/animal host and the organism''s survivability in natural environments are compared. In addition, the effect of the diversity and community structure of the indigenous microbiota on the fate of invading E. coli populations in the open environment is discussed. Such a relationship is of importance to our knowledge of both public and environmental health.     

Characterization of O-glycosidically linked oligosaccharides of rat erythrocyte membrane sialoglycoproteins

The carbohydrate units of the rat erythrocyte membrane sialoglycoprotein rSGP-4 [Edge, A. S. B., & Weber, P. (1981) Arch. Biochem. Biophys. 209, 697-705] have been characterized. All of the carbohydrate of this Mr 19,000 glycoprotein occurs in O-glycosidic linkage to the peptide; following alkaline borohydride treatment and chromatography on Bio-Gel P-2, sialic acid containing oligosaccharides terminating in N-acetylgalactosaminitol were obtained. Their structures were determined by compositional analysis, exoglycosidase digestions, alkaline sulfite degradation, and periodate oxidation. The oligosaccharides were characterized for molecular weight and linkage by direct chemical ionization and gas-liquid chromatography/mass spectrometry, respectively. The structures are proposed to be NeuAc alpha 2----3Gal beta 1----3GalNAc-ol, Gal beta 1----3(NeuAc alpha 2----6)GalNAc-ol, NeuAc alpha 2----3Gal beta 1----3(NeuAc alpha 2----6)GalNAc-ol, and NeuAc alpha 2----3Gal beta 1----3(NeuAc alpha 2----3Gal beta 1----4GlcNAc beta 1----6)GalNAc-ol. Two of the N-acetylglucosamine-containing hexasaccharides were present per molecule of rSGP-4 along with two trisaccharides and seven tetrasaccharides.     

The binding of folyl polyglutamates by hemoglobin

Pteroyl polyglutamates bind to hemoglobin with an affinity which leaves only a minor fraction of red cell folate in the free state. This could serve as a regulating mechanism for protein synthesis in the differentiating erythroblast.     

Preferential expression of cellular retinoic acid binding protein in a subpopulation of neural cells in the developing mouse embryo

The cellular retinoic acid binding protein is thought to be involved in the retinoic-acid-mediated signal transduction pathway. We have isolated the mouse cellular retinoic acid binding protein cDNA from an embryonal-carcinoma-derived cell line by using differential cDNA cloning strategies. In situ hybridization on sections of mouse embryos of various developmental stages indicated that the cellular retinoic acid binding protein gene, which we localized on mouse chromosome 9, is preferentially expressed in a subpopulation of neurectodermal cells. This restricted expression pattern suggests an important role for cellular retinoic acid binding protein in murine neurogenesis.     

Effect of altered sink: source ratio on photosynthetic metabolism of source leaves

When seven crop species were grown under identical environmental conditions, decreased sink:source ratio led to a decreased photosynthetic rate within 1 to 3 days in Cucumis sativus L., Gossypium hirsutum L., and Raphanus sativus L., but not in Capsicum annuum L., Solanum melongena L., Phaseolus vulgaris L., or Ricinus communis L. The decrease was not associated with stomatal closure. In cotton and cucumber, sink removal led to an increase in starch and sugar content, in glucose 6-phosphate and fructose 6-phosphate pools, and in the proportion of ¹⁴C detected in sugar phosphates and UDPglucose following ¹⁴CO₂ supply. When mannose was supplied to leaf discs to sequester cytoplasmic inorganic phosphate, promotion of starch synthesis, and inhibition of CO₂ fixation, were observed in control discs, but not in discs from treated plants. Phosphate buffer reduced starch synthesis in the latter, but not the former discs. The findings suggest that sink removal led to a decreased ratio inorganic phosphate:phosphorylated compounds. In beans ¹⁴C in sugar phosphates increased following sink removal, but without sucrose accumulation, suggesting tighter feedback control of sugar level. Starch accumulated to higher levels than in the other plants, but CO₂ fixation rate was constant for several days.     

Root-Zone-Specific Oxygen Tolerance of Azospirillum spp. and Diazotrophic Rods Closely Associated with Kallar Grass

The effect of oxygen on N₂-dependent growth of two Azospirillum strains and two diazotrophic rods closely associated with roots of Kallar grass (Leptochloa fusca) was studied. To enable precise comparison, bacteria were grown in dissolved-oxygen-controlled batch and continuous cultures. Steady states were obtained from about 1 to 30 μM O₂, some of them being carbon limited. All strains needed a minimum amount of oxygen for N₂-dependent growth. Nitrogen contents between 10 and 13% of cell dry weight were observed. The response of steady-state cultures to increasing O₂ concentrations suggested that carbon limitation shifted to internal nitrogen limitation when N₂ fixation became so low that the bacteria could no longer meet their requirements for fixed nitrogen. For Azospirillum lipoferum Rp5, increase of the dilution rate resulted in decreased N₂ fixation in steady-state cultures with internal nitrogen limitation. Oxygen tolerance was found to be strain specific in A. lipoferum with strain Sp59b as a reference organism. Oxygen tolerance of strains from Kallar grass was found to be root zone specific. A. halopraeferens Au 4 and A. lipoferum Rp5, predominating on the rhizoplane of Kallar grass, and strains H6a2 and BH72, predominating in the endorhizosphere, differed in their oxygen tolerance profiles. Strains H6a2 and BH72 still grew and fixed nitrogen in steady-state cultures at O₂ concentrations exceeding those which absolutely inhibited nitrogen fixation of both Azospirillum strains. It is proposed that root-zone-specific oxygen tolerance reflects an adaptation of the isolates to the microenvironments provided by the host plant.     

Cyclic glucans produced by Agrobacterium tumefaciens are substituted with sn-1-phosphoglycerol residues

In a previous study (Miller, K.J., Kennedy, E.P. and Reinhold, V.N. (1986) Science 231, 48-51) it was reported that the biosynthesis of periplasmic cyclic beta-1,2-glucans by Agrobacterium tumefaciens is strictly osmoregulated in a pattern closely similar to that found for the membrane-derived oligosaccharides of Escherichia coli (Kennedy, E.P. (1982) Proc. Natl. Acad. Sci. USA 79, 1092-1095). In addition to the well-characterized neutral cyclic glucan, the periplasmic glucans were found to contain an anionic component not previously reported. Biosynthesis of the anionic component is osmotically regulated in a manner indistinguishable from that of the neutral cyclic beta-1,2-glucan. We now find that the anionic component consists of cyclic beta-1,2-glucans substituted with one or more sn-1-phosphoglycerol residues. The presence of sn-1-phosphoglycerol residues represents an additional, striking similarity to the membrane-derived oligosaccharides of E. coli.     

The role of the carboxy-terminal membrane-spanning fragment in the biogenesis of Escherichia coli K12 outer membrane protein PhoE

Summary PhoE protein of Escherichia coli K12 is an outer membrane protein which is supposed to span the membrane sixteen times. By creating a deletion which removes the last membrane-spanning fragment and studying the localization of the truncated PhoE, we show that this fragment is indispensable for trimerization and outer membrane localization. In addition, circumstantial evidence for the proposed topology model of the protein was obtained. An insertion mutation in a region supposed to be cell surface-exposed, interferes with the binding of a monoclonal antibody which recognizes a cell surface-exposed epitope of the protein.